ISLAMABAD, Aug 6 (Reuters) - Pakistan's civilian government is bracing for a wave of protests this month, days after the military took responsibility for securing the capital amid the threat of militant attacks and the spectre of a political showdown.

Some Pakistanis fear that the country's traditionally powerful military, which has ruled Pakistan for about half of its history, may use the protests to buttress its position at the expense of the fledgling civilian government.

"It's not something that the military has choreographed, it is just benefiting from the civilian government's weakness," said columnist Ejaz Haider.

Activist and cleric Tahir ul-Qadri, known for his passionate monologues, will hold a protest on Aug. 10. He has vowed to topple and jail government ministers by month-end.

Charismatic cricketer turned opposition politician Imran Khan has also announced that his supporters will hold a sit-in in the capital on Aug. 14. He wants the government to resign and new elections to be held.

"This will be the biggest demonstration in the history of Pakistan," Khan told a news conference late on Tuesday.

Both Qadri and Khan have at times been seen by some Pakistanis as close to the military, or even as being used by the military to pressure the government. Both of them deny that and the military denies such meddling in politics.

Pakistan has weathered such protest marches before. Last year tens of thousands of Qadri supporters camped out along the main road in the capital for four days.

Yet the upcoming protests have sent ripples of unease through the nuclear-armed nation of 180 million because of its history of coups, corruption and militancy.

The stock market has dipped and the government has postponed a planned increase in electricity rates.

MILITARY RELATIONS

Prime Minister Nawaz Sharif's landslide election win last year marked the first time one elected government had handed power to another since independence from Britain in 1947.

Just after elections, his government pursued policies that were known to have angered the military.

He promoted better ties with neighbouring India, whom the army still considers to be Pakistan's biggest threat. Sharif also put Pervez Musharraf, the former army chief and president, who deposed him in 1999, on trial.

There was also disagreement on how to handle militants attacking the state with the army favouring military action and the government holding out hope for peace talks. The army eventually won the argument and launched an offensive in June.

Last week, the government handed responsibility for securing the capital to the military, a move Khan insisted was an attempt to co-opt the army and intimidate protesters.

"The government is trying to protect itself by bringing in the army and hiding behind it," he said. "It is totally undemocratic."

The ruling party strongly denies his accusation.

It says troops were deployed for 90 days outside key buildings in Islamabad to prevent Pakistani Taliban revenge attacks for the military offensive against them.

"This is purely to prevent Taliban blowback," said Senator Tariq Azeem. "It's nothing to do with the opposition, they are just trying to make themselves seem important."

"The government is not going to fall."

Whatever the reason for the government's call on the military to take over security in Islamabad, many Pakistanis have seen it as an indication of weakness on the part of the government.

"You had a prime minister who was determined to keep the military out (of politics) but now he has invited them in," said the columnist, Haider.

POVERTY, POWER AND CORRUPTION

Both Khan and Qadri are protesting over issues with relatively narrow national appeal. Khan is urging electoral reforms and investigations into last year's poll. Qadri is protesting after police killed fourteen of his supporters in clashes in June.

"If police enter your home, barge into their houses in a mob and crack down on them," Qadri urged supporters at a news conference on Sunday. "We will take revenge for all our martyrs."

Both men are also hoping to capitalize on widespread public frustration over the government's slow pace at tackling endemic power shortages, widespread poverty and corruption.

Thousands of extra police have been ordered to block sections of the capital with shipping containers and barbed wire. Yet many think the government should just let the marches proceed peacefully.

"If the government tries to stop this, it will just get nasty," said radio talk-show host Murtaza Solangi.

"They should just say, come ... now how long do you want to sit in the street in this 45 degree heat?" (Editing by Clarence Fernandez)